Two recent studies published in Environmental Health Perspectives evaluated the differences between results of the same experiments with nanomaterials when conducted by different laboratories. In each study, multiple laboratories tested toxicity of specific nanomaterials (titanium dioxide for a rodent pulmonary study, and zinc oxide, titanium dioxide and carbon nanotubes in an in vitro study).

The rodent pulmonary responses study concluded that “similar patterns of neutrophilia and pathology” exist in both rats and mice. Results of this study also indicated that laboratories varied in the degree of neutrophilia found, but that “similar findings of relative potency for the three types of [titanium dioxide] were found across all laboratories, thus providing greater confidence in these inter-laboratory comparisons.” The in vitro study indicated that mechanismlinked bioreactivity assays improve results when added to cytotoxicity assays.

The rodent pulmonary response study authors observed that nanomaterial toxicity studies are often difficult to compare because of “inconsistencies in health outcomes and/or toxic thresholds.” They indicated that additional barriers to predictable, repeatable and reliable results for nanomaterial exposure studies include (i) differences between batches of a given nanomaterial; (ii) inherent interlaboratory comparison difficulties; (iii) agglomeration of the nanoparticles, which can change toxicity; (iv) different methods and duration of dosing and dose level; and (iv) different methods of nanomaterial handling before testing.